From U.S. Pat. No. 5,732,467 a method for repairing surface cracks is known, whereas the substrate consisting of a superalloy features a directionally solidified structure. The cleansed crack is filled with the substrate material. Then the coated crack is exposed for a certain period of time to increased temperature and isostatic pressure, without the microstructure of the substrate being changed.
U.S. Pat. No. 5,666,643 discloses a method performed by means of brazing for repairing components consisting of cobalt and nickel-based superalloys. In this method a brazing material consisting of two components is used. One component of said brazing material forms the (actual) braze alloy, and its other component is formed by particles which are high-melting and which are either single-crystalline, directionally solidified or polycrystalline. In this composition, the microstructure of the repaired crack varies from that of the substrate, adversely affecting the interior space of the filled cracks, especially if the cracks are positioned in areas having stress concentrations.
Similar problems result from repair methods in which the microstructure of the substrate is not reconstructed, as, for instance, in the context of methods known from U.S. Pat. No. 4,381,944 or U.S. Pat. No. 5,437,737. In these methods each braze alloy is provided with an additive material in order to increase the solidity of the filled gap.
The method disclosed in U.S. Pat. No. 5,156,321 takes a different approach in that it uses a sintering process in order to make the repair more effective.
Two similar brazing methods are disclosed in U.S. Pat. No. 4,830,934 and U.S. Pat. No. 5,240,490 which are to be used for polycrystalline or directionally solidified superalloys, as described in U.S. Pat. No. 4,288,247. Here, the repair system consists of at least three different powdered metals. These different powdered metals fulfill different functions. The powdered metal of the first group are high-melting and have a relatively high proportion of Mo, Re and W. During the brazing process, these powdered metals are not melting, or are melting only partially. The powdered metals of a second and the remaining third group cause the brazing system to have a respective flow behavior. Here, the powdered metals of the second group contain B and/or Si as melting point reducers, and the powdered metals of the third group exhibit eutectic compositions and support as liquid phase the filling during the brazing process. Solidification is caused by an isothermal brazing process, followed by a gradual diffusion cycle, achieving, however, no single-crystalline filling of the gap. Here, modular conception allows for flexible handling of the microstructure of the gap and the mechanical characteristics, which definitely achieve the characteristics of the substrates.
Similar modular conception is disclosed in US 2002/0157737 A1. According to this disclosure, a low-melting powder, which contains up to 1% Ti, W, Re, Mo, Nb, Hf, Pd, Pt, Ir, Ru, C, Si and/or Zr, is mixed with at least one high-melting powder. Here, the brazing temperature amounts to 1260° C. (10-40 min.), again followed by a gradual diffusion cycle. It appears that the creep-rupture strength is close to that of the substrate.
According to the disclosure of EP 1 226 896 A2, René 80 powder is mixed with a ternary eutectic braze alloy, which contains approximately 15% Cr, 3.5% B and additionally up to 1.5% Fe. The mixing ratio amounts to 65:35 in favor of René 80. The brazing temperature ranges between 1175° C. and 1215° C. and is maintained for approximately 20 minutes. This produces a brazed seam having a polycrystalline microstructure. Different techniques can be used to apply the repair part to the component, for example, paste, putty or pre-sintered sheets. Pre-sintered sheets, for example, can be produced in such a way that superalloy metal sheets are produced in powder-metallurgical manner, as disclosed in GB 2153845 A.
U.S. Pat. No. 6,325,871 discloses an isothermal brazing cycle by means of which components consisting of cast superalloys can be connected. For this purpose, foils are used which have a boracic concentration of between 1 and 3 wt %.
A similar method is known from U.S. Pat. No. 6,508,000 regarding inserts. This pamphlet discloses a brazing process (limited to gap widths of up to 25 μm) by temporarily controlled liquid phase by means of which turbine blades and guide vanes can be repaired.
A further approach is disclosed in U.S. Pat. No. 6,968,991 regarding single-crystalline components. Here, the brazing material is applied in the form of a viscous mass (paint), consisting of brazing material, additive material, binding agent and a substrate, to the crack having a maximum width of 0.05 mm, which has previously been closed and spot welded. The brazing process in itself requires up to 20 minutes and is performed at a temperature of 1204° C. After a subsequent process of heat dissipation to 816° C. another heating process to 1204° C. takes place, so that the melting point reducers from the crack diffuse into the base material.
U.S. Pat. No. 6,629,368 discloses especially an isothermal brazing repair of single-crystalline turbine blades which seems to reconstruct a single-crystalline structure in the brazed areas. According to U.S. Pat. No. 6,629,368, this composition has the disadvantage that it involves the danger of damaging the base material. It is also inefficient because it involves long processing times.
U.S. Pat. No. 6,629,368 also discloses a method according to which an isothermal epitaxic process of curing cracks on single-crystalline materials has been provided.
The compositions known from U.S. Pat. No. 4,830,934 or U.S. Pat. No. 5,240,491 or U.S. Pat. No. 5,732,467 or U.S. Pat. No. 5,666,643 or U.S. Pat. No. 4,381,944 or U.S. Pat. No. 5,437,737 have the disadvantage that, after the repair, the components do not have the original mechanical strength, oxidation resistance and re-melting temperature or that, after the repair, the quality of the components has considerably deteriorated with regard to the above-mentioned criteria.
Against this background, the invention has the objective of providing an appropriate possibility to join and/or repair components in the field of aircraft engines or turbines. By means of this possibility the mechanical and physical characteristics in the range of joining and repairing will not be adversely affected, or at least only to a relatively small degree.